Generally, an endoscope is composed of a manipulating head and an elongated insertion instrument which is extended forward from the manipulating head for introduction into a body cavity in need of an endoscopic examination or treatment. In endoscopic examinations and treatments, an aspiration mechanism on an endoscope is resorted to for the purpose of observing an intracavitary site of interest in a clearly visible state. Namely, in case an intracavitary site under observation or treatment is covered with internal filth or body fluids like blood to such a degree as to make it difficult to observe the intracavitary site in question clearly, an aspiration mechanism is turned on to suck out covering internal filth and body fluids. In this regard, it has been the usual practice to utilize as an aspiration passage a tool introduction channel which is provided on an endoscope for introduction of forceps or other surgical instruments into a body cavity. In some cases, an aspiration passage is provided separately from a tool introduction channel. Anyway, an endoscopic aspiration device including an aspiration valve and a valve operating member is mounted on a manipulating head of an endoscope. The aspiration valve is connectable to a proximal aspiration passage from a suction source, so that aspiration can be carried out for a necessary time period by manipulation of the aspiration valve operating member.
By the way, not only aspiration passages including a tool introduction channel of an endoscope and interiors of an aspiration valve but also interiors of a proximal aspiration passage on the side of a suction source unavoidably get contaminated by the use of an endoscopic aspiration device. Therefore, all of contaminated aspiration passages in transit have to be completely washed and disinfected before using the endoscope again. However, an aspiration valve which is adapted to bring aspiration passages into and out of communication with a proximal aspiration passage on the side of a suction source is complicate in construction, so that it has been extremely difficult to completely wash the entire routes of aspiration through and to and from an aspiration valve which is mounted on a manipulating head of an endoscope.
With a view to solving the problem as mentioned above, for example, Patent Literature 1 below discloses an aspiration valve which is improved in washability. In Patent Literature 1, an aspiration passage which is provided internally of an elongated insertion rod member as far as an opening at a fore distal end of the insertion rod member is connected with a proximal aspiration passage on the side of a suction source at a point on a manipulating head of the endoscope. In order to connect and disconnect the aspiration passage to and from the proximal aspiration passage, a proximal end of the aspiration passage is connected to a valve casing within a housing of the manipulating head, and an external valve assembly unit is disconnectibly connected to the valve casing. The external valve assembly unit is constituted by a valve guide member which is adapted to be disconnectibly connected to the valve casing, and a valve member to be slidably fitted in the valve guide member. A connector pipe is provided at a lateral side of the valve guide member for disconnectibly connecting thereto a proximal aspiration passage on the side of a suction source.
One end of the valve member, i.e., an end away from a valve body at the other end, is arranged to serve as an aspiration trigger portion which is designed to be manipulated by a finger of an operator's hand which grips the manipulating head of the endoscope. The valve body is located in the valve casing, normally blocking communication between the aspiration passage and proximal aspiration passage. As the aspiration trigger portion is pushed in, the valve body is caused to slide along inner surfaces of the valve casing to open the communication between the aspiration passage and the proximal aspiration passage. As a result, the vacuum pressure from the proximal aspiration passage comes to prevail in the aspiration passage to apply a suction force to an opening at the distal end of the insertion rod member.
The aspiration takes an internal route through the insertion rod member and as far as the manipulating head of the endoscope, and then takes an external route which is led out from a housing of the manipulating head. A flexible tube of a proximal aspiration passage, i.e., a passage on the side of a suction source, is connected to a connector pipe which is extended out from the above-mentioned valve guide, which is projected on the housing of the manipulating head. When an operator grips the manipulating head in his or her hand to operate the endoscope, however, the connector pipe and the flexible proximal aspiration passage are often found obstructive of the operation of the endoscope. For this reason, the valve assembly unit is arranged to be turnable relative to the valve casing, permitting to turn the connector pipe and the flexible proximal aspiration passage out of the way of manipulation of the endoscope.
The above-mentioned valve assembly unit is disconnectible from the valve casing. After each use, the valve assembly unit is dismantled from the valve casing and a cleaning brush is inserted into the aspiration passage for washing same completely. The flexible proximal aspiration passage which is connected to the valve assembly unit and connector pipe can be reused after washing or may be simply discarded and replaced by a new one.    Patent Literature 1 Japanese Laid-Open Patent Application 2007-252589